Hoist control system having a photocoupled pendant

ABSTRACT

A variable hoist speed control system has a pendant control handle for establishing a desired hoist speed signal in a remotely mounted hoist associated control which controls the actual hoist speed. The signal from the pendant control handle is electrically isolated from the hoist control by a photocoupling assembly to eliminate noise and interference signals picked up by the pendant from reaching the hoist control. The pendant control handle provides a linear signal indicative of desired hoist speed to the photocoupling assembly which in turn provides a logarithmic output signal to the hoist control indicative of desired hoist speed to allow a more accurate hoist speed control at slower hoist speeds.

United States Patent 11 1 Freeman 1 1 Aug. 26, 1975 1 1 HOIST CONTROL SYSTEM HAVING A PHOTOCOUPLED PENDANT [75] Inventor:

[73] Assignee: Eaton Corporation, Cleveland. Ohio [22] Filed: Dec. 26, 1973 [211 App]. No.: 427,973

Harvey L. Freeman, Brinkley, Ark.

3.777.188 12/1973 Mazur 323/21 Primary Examiner-G. Z. Rubinson Attorney, Agent, or FirmTeagno & Toddy [57] ABSTRACT A variable hoist speed control system has a pendant control handle for establishing a desired hoist speed signal in a remotely mounted hoist associated control which controls the actual hoist speed. The signal from the pendant control handle is electrically isolated from the hoist control by a photocoupling assembly to eliminate noise and interference signals picked up by the pendant from reaching the hoist control. The pendant control handle provides a linear signal indicative of desired hoist speed to the photocoupling assembly which in turn provides a logarithmic output signal to the hoist control indicative of desired hoist speed to allow a more accurate hoist speed control at slower hoist speeds.

13 Claims, 4 Drawing Figures HOIST CONTROL SYSTEM HAVING A PHOTOCOUPLED PENDANT BACKGROUND OF THE INVENTION 1. Field of the Invention:

This invention relates to hoist control systems generally and particularly to variable speed hoist controls having a pendant control remotely mounted and electrically isolated from a main hoist control.

2. Description of the Prior Art:

In hoist control systems utilizing a remotely mounted pendant control handle the long expanse of cable connecting the pendant to the main hoist control acts as an antenna for picking up various noise and interference signals prevalent in the industrial background of most hoist installations. This noise and interference is superimposed on the electrical cable connecting the pendant control to the main hoist control and is transmitted to the main hoist control along with the control signal originating from the pendant control. Clearly the operation of the hoist is adversely affected by these Super imposed noise and interference signals.

To prevent the transmission of such noise and interference signals to the main hoist control, some control systems use a shielded cable for the electrical connection of the pendant control to the main hoist control to isolate the noise and interference signals from the cable. Although the shielded cable is effective in isolating the cable and hence the main control system from noise and interference signals, the shielded cable is expensive, bulky and insufficiently flexible to allow easy manipulation of the pendant control by a hoist operator.

Other systems use a magnetic coupling such as a variable core transformer to connect the lead cable from the pendant control to the main hoist control. Such a magnetic coupling electrically isolates the pendant control from the main hoist control and prevents the noise and interference signals from reaching the main hoist control. However, such an isolation technique requires an AC signal from the pendant control to be applied to one side of the magnetic coupling transformer before a usable output signal will be induced in the secondary winding of the transformer which is electrically connected to the main hoist control. A hoist control system utilizing the above described isolation technique is best described in US. Pat. No. 3,402,335 which issued Sept. 17, 1968 to A. H. Smith et al and the reader is referred thereto for a more detailed explana tion.

SUMMARY OF THE INVENTION The present invention solves the previously men tioned problems and limitations of the described prior art control systems and others by providing a hoist control system wherein a pendant control is remotely mounted from a main hoist control and is electrically isolated therefrom by a photocoupling connection between the pendant control and the main hoist control.

This hoist control system utilizes a pendant control which is remotely mounted from the hoist, the hoist motor and the hoist motor control. The pendant control establishes a reference signal which is indicative of desired hoist motor operation and transmits this reference signal to a photocoupling unit connecting the pendant control to the hoist motor control. The photocoupling unit in turn transmits the reference signal free of any noise or interference signals to a control signal unit of the hoist motor which establishes a control signal for operating the hoist motor control in response to the reference signal from the pendant control. Since the pres ent control system utilizes a photocoupling unit to connect the pendant control to the main hoist motor control, any noise and interference signals picked up by the cable connection of the pendant control are effectively isolated from the main hoist motor control. Thus there is no need for using shielded cable for the pendant control connecting cable. Further, a DC signal may be established by the pendant control as the reference signal since the photocoupling unit will respond to DC as well as AC level input signals.

The photocoupling unit may generally include a light source connected to the pendant control and a receiver connected to the main hoist control. The light source emits a variable intensity light source proportional to the reference signal provided by the pendant control. The receiver is sensitive to the light intensity of the light source and establishes a control signal which is non-linear with respect to the reference signal provided by the pendant control. Thus a logarithmic response may be obtained from the receiver in response to a linear reference signal provided by the pendant control. This allows the pendant control to have increased sensitivity over a certain range of hoist speed. As an example, the slower hoist speeds, which are more difficult to control, may be matched to correspond with the increased sensitivity range of the receiver output.

From the foregoing it will be appreciated that the present invention provides numerous features which are not found in known prior art devices and which allow for improved construction and operation thereover.

One feature of the present invention is to provide a pendant control for a hoist which is electrically isolated from the main hoist control to prevent noise and interference signals picked up by the pendant control from being transmitted to the main hoist control.

Another feature of the present invention is to provide a hoist control system wherein a linear reference signal from the pendant control to the photocoupling unit results in a non-linear output signal from the photocoupling unit to the main hoist control.

These and other features of the present invention will become clearer upon reviewing the following description of the preferred embodiment in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of the hoist control system of the present invention.

FIG. 2 is an expanded view of the circuitry of the pendant control and its connection to the photocoupling unit shown in FIG. 1.

FIG. 3 is a graphical representation of the voltage to the light source of the photocoupling unit and the resistance response of the receiver of the photocoupling unit.

FIG. 4 is a graphical representation of the hoist motor speed response to the dial rotation of the pendant control.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein the showings are only intended to be illustrative of a preferred embodiment of the present invention, FIG. 1 shows a hoist control system for controlling the speed of a hoist motor from a pendant control 14 remotely mounted from the hoist motor 10. The pendant control 14 is electrically connected to a photocoupling unit 16 which acts to electrically isolate the pendant control 14 from a photocoupling unit 16 associated hoist motor control system 18 mounted proximately to the hoist motor 10. The photocoupling unit 16 while electrically isolating the pendant control 14 from the hoist motor control 18 still provides an optical coupling between the pendant control 14 and the hoist motor control 18.

Referring to FIGS. 1 and 2, the pendant control 14 is constructed to be easily held in the hand of a hoist operator who can control the direction and speed of the hoist motor 10 by appropriate manual controls mounted on a face of the pendant control 14. The motor 10 speed is controlled by the appropriate rotation of a dial knob 22 in either the clockwise direction for increased motor 10 speed or in the counterclockwise direction for decreased motor 10 speed. The direction of motor 10 rotation and consequently the direction of chain 12 movement is controlled by push buttons 24 and 26. Thus depressing of the push button 24 will cause the chain 12 to be raised at a speed set by the knob 22 and depressing of the push button 26 will cause the chain 12 to be lowered at the speed set by the knob 22.

The knob 22 controls the speed of the motor 10 by establishing a variable reference signal in the pendant control 14 which signal is transmitted to the photocoupling unit 16 along line 28. As may be best seen with reference to FIG. 2, the reference signal is varied through a potentiometer 30 whose sliding arm 32 moves along a resistor R in response to rotation of the knob 22. The knob 22 is mechanically coupled to the sliding arm 32 through a coupling 34 which allows the sliding arm 32 to proportionately traverse the full extent of the resistor R upon a 300 rotation of the knob 22 to thereby vary the voltage applied by a voltage source V to the photocoupling unit 16. A scaling resistor R is series connected with the potentiometer 30 and the photocoupling unit 16 to scale the voltage V down to a level which is usable by the photocoupling unit 16.

The photocoupling unit 16 has a light source 36 and a photoresistive receiver 38 assembled in a light tight case to prevent the actuation of the photoresistive receiver by stray light not originating from the light source 36. A Raysistor may be used as the photocoupling unit 16 and such a Raysistor unit may be obtained from Raytheon Corporation.

The light source 36 of the photocoupling unit 16 is electrically series connected to the potentiometer 30 through line 28 and produces light from an incandescent filament having an intensity which varies with variable voltage applied to the filament. This voltage may be either AC,or DC voltage. Since the incandescent filament has a slow response to voltage change, electrical noise and interference signals of short duration, which are prevalent in environments using hoists, are not sensed by the filament and are thereby effectively eliminated.

The photoresistive element 38 is electrically isolated from the light source 36 but is responsive to light from the light source 36. This response results in the element 38 changing its electrical resistance in response to the intensity of the light from the light source 36. As may be seen with reference to FIG. 3, the resistance of the photoresistive element 38 will change logarithmically with a linear voltage change applied across the filament of the light source 36. This characteristic response of the photoresistive element 38 allows a linear reference voltage change produced by the knob 22 in the potentiometer 30 to be converted to a logarithmic change in the output of the photoresistive element 36 oi photocoupling unit 16. Improved slow motor speed control is obtained thereby, as will be disclosed later.

The photoresistive element 38 is electrically series connected to the voltage source V and resistor R to form a voltage divider circuit with R As the resistance of the element 38 changes with the intensity of the light source 36, a variable control signal, dependent upon the reference signal from the pendant 14, is supplied to the hoist motor control circuit 18 along line 40 which is indicative of desired hoist motor speed.

The hoist motor control circuit 18 compares the signal indicative of desired hoist motor speed with a signal indicative of actual hoist speed and establishes a control signal to change the actual motor speed to desired motor speed whenever there is a difference between the compared signals. To accomplish this, a tachometer 42 senses the actual speed of the hoist motor 10 and conducts a signal indicative of actual motor 10 speed to an operational amplifier 44 by line 46. The operational amplifier 44 is also connected to line 40 and compares the signal indicative of actual motor speed conducted along line 46 with the reference motor speed signal conducted along line 40 to provide an error signal along line 48 to a logic circuit 50. The logic circuit 50 provides a signal to a thyristor assembly 52 along line 54 which varies the firing angle of the thyristors in the thyristor assembly to vary the power supplied from an AC source 56 to the motor 10 by way of the thyristor assembly 52. Logic circuits and thyristor assemblies for providing variable power to a motor are well known to those skilled in the art and will not be discussed in detail herein. An example of such circuitry may be found in US. Pat. No. 3,402,335 issued Sept. 17, 1968 to A. H. Smith et al and the reader is referred thereto for a more detailed explanation of the structure and operation of such circuitry.

From the foregoing it will be seen that hoist operation is accomplished in the following manner. The operator selects the speed and direction of the hoist motor by appropriately dialing the speed on the knob 22 and the direction by depressing either of buttons 24 or 26. The knob 22 changes the position of potentiometer 30 to establish a reference signal to the light source 36 which energizes the filament to a particular intensity, while depressing either button 24 or 26 will send a signal to the thyristor assembly 52 by way of line 58 to actuate either the forward or reverse direction thyristors. The photoresistive element 38 changes resistance in response to the light intensity of the source and thereby provides an electrically isolated signal to the operational amplifier 44 which signal is indicative of the desired hoist motor 10 speed. The operational amplifier compares this reference signal with a feedback signal from the motor 10 indicative of the actual motor speed and establishes a control signal in relation to the difference in compared signals. This control signal is received by a logic circuit which fires the appropriate directional thyristor assembly causing power to be applied to the motor of a polarity determining the motor direction as chosen by switches 24 and 26. As the speed of the motor 10 increases, the feedback signal to the operational amplifier 44 increases and the control signal therefrom decreases. The logic circuit 50 changes the firing angle of the thyristor assembly 52 to decrease the power transmitted to the motor 10 until the motor 10 is running at the desired speed. Since the knob 22 provides a linear reference voltage signal to the light source 36 while the photoresistive element 38 reacts to the light source to establish a logarithmic output reference signal to the control amplifier 44, the ac tual speed of motor 10 is a logarithmic function of the speed indicated on the knob 22, as may be seen with reference to FIG. 4. This relationship allows the control of the critical slower /a of actual motor speed through approximately 200 of the knob 22 rotation. The remaining 100 of knob 22 rotation is left to control the less critical higher motor speed.

It may thus be seen that the present hoist control system allows the pendant control to be remotely located from the hoist and the hoist speed control without transmitting noise and interference signals from the pendant control to the hoist speed control by virtue of the unique photocoupling between the pendant control and the hoist speed control. Because of the logarithmic response of the present photocoupling system, improved low speed hoist control is also made possible.

Certain modifications and improvements will occur to those skilled in the art upon reading this specification. It will be understood that such modifications and improvements were deleted for the sake of conciseness and readability but that they are included within the scope of the claims.

I now claim:

1. A hoist control system comprising:

a motor for operating the hoist;

motor control means, mounted proximately to the hoist, for operating said motor of said hoist in response to a control signal to said motor control means;

pendant control means, remotely mounted from the hoist, for establishing a reference signal indicative of desired hoist motor operation;

control signal means associated with said motor control means for establishing said control signal in said motor control means in response to the reference signal in said pendant control;

connecting line means for electrically connecting said remotely mounted pendant control means to the hoist; and

photocoupling means mounted proximately to the hoist and connected to said connecting line means and to said control signal means to prevent any noise and interference signals picked up by said connecting line means from being transmitted to said control signal means.

2. A hoist control system as set forth in claim 1 wherein said photocoupling means includes:

a light source mounted proximately to said control signal means and electrically connected to said re motely mounted pendant control means to emit a light source in response to the reference signal from said pendant control means; and

a photoresistive element mounted proximately to said light source to be responsive to light from said light source, said photoresistive element being electrically connected to said control signal means to transmit said reference signal to said control signal means.

3. A hoist control system as set forth in claim 2 wherein said light source emits a variable intensity light in direct proportion to a voltage signal applied to said light source and wherein said photoresistive material logarithmically varies in resistance in response to the variable intensity light emitted by said light source.

4. A hoist control system as set forth in claim 2 wherein said light source is an incandescent filament lamp being unresponsive to intermittent voltage signals of short duration as compared to the duration of said reference signal to make said lamp insensitive to noise and interference signals thereby.

5. A hoist control system as set forth in claim 3 wherein said pendant control means includes:

a hand-held control assembly having a manual adjustment knob;

a potentiometer connected to the manual knob of said hand control assembly to provide a variable voltage signal in response to manual adjustment of the knob; and

said light source being connected to said potentiometer to provide the variable intensity light in re sponse to manual adjustment of the knob of said hand control assembly.

6. A hoist control system as set forth in claim 5 including:

feedback means for providing a feedback signal of actual hoist motor operation; and wherein said control signal means includes an operational amplifier having one input connected to the photoresistive element of said photocoupling means and a second input connected to the feedback signal of said feedback means to compare the signals from the first and the second input and, thereby, establish the control signal.

7. A hoist control system as set forth in claim 6 wherein said operational amplifier is a difference amplifier for establishing the control signal in proportion to the difference between the feedback signal and the reference signal.

8. A hoist control system providing a non-linear control signal for controlling a hoist motor in response to a linear reference signal from a pendant control comprising:

manual means for establishing a voltage reference signal directly proportional to a manual adjustment of the pendant control;

light source means connected to the pendant control to emit a variable intensity light proportional to the reference signal of said manual means; and

receiver means logarithmically responsive to the light of said light source means for establishing a control signal in response to the variable intensity light of said light source means, the control signal of said receiver means thereby being established in a nonlinear relation to a linear manual adjustment of said manual means to drive said hoist motor at an increased speed in response to an increased voltage reference signal.

9. A hoist control system as set forth in claim 8 in cluding a potentiometer mounted in the pendant control to provide a variable voltage signal from the pendant control and wherein said manual means includes an adjustment knob mounted to the pendant control to adjust the voltage signal from said potentiometer in a linear relationship to the movement of the knob of said manual means.

10. A hoist control system as set forth in claim 9 wherein said receiver means includes a variable resistance material whose resistance changes logarithmically in response to a linear change of the knob of said manual means.

11. A hoist control system as set forth in claim 10 wherein said light source means includes an incandescent filament lamp which is unresponsive to intermittent voltage changes in said reference signal induced by noise and interference signals being superimposed on said reference signal.

12. A hoist control system as set forth in claim 8 in- 

1. A hoist control system comprising: a motor for operating the hoist; motor control means, mounted proximately to the hoist, for operating said motor of said hoist in response to a control signal to said motor control means; pendant control means, remotely mounted from the hoist, for establishing a reference signal indicative of desired hoist motor operation; control signal means associated with said motor control means for establishing said control signal in said motor control means in response to the reference signal in said pendant control; connecting line means for electrically connecting said remotely mounted pendant control means to the hoist; and photocoupling means mounted proximately to the hoist and connected to said connecting line means and to said control signal means to prevent any noise and interference signals picked up by said connecting line means from being transmitted to said control signal means.
 2. A hoist control system as set forth in claim 1 wherein said photocoupling means includes: a light source mounted proximately to said control signal means and electrically connected to said remotely mounted pendant control means to emit a light source in response to the reference signal from said pendant control means; and a photoresistive element mounted proximately to said light source to be responsive to light from said light source, said photoresistive element being electrically connected to said control signal means to transmit said reference signal to said control signal means.
 3. A hoist control system as set forth in claim 2 wherein said light source emits a variable intensity light in direct proportion to a voltage signal applied to said light source and wherein said photoresistive material logarithmically varies in resistance in response to the variable intensity light emitted by said light source.
 4. A hoist control system as set forth in claim 2 wherein said light source is an incandescent filament lamp being unresponsive to intermittent voltage signals of short duration as compared to the duration of said reference signal to make said lamp insensitive to noise and interference signals thereby.
 5. A hoist control system as set forth in claim 3 wherein said pendant control means includes: a hand-held control assembly having a manual adjustment knob; a potentiometer connected to the manual knob of said hand control assembly to provide a variable voltage signal in response to manual adjustment of the knob; and said light source being connected to said potentiometer to provide the variable intensity light in response to manual adjustment of the knob of said hand control assembly.
 6. A hoist control system as set forth in claim 5 including: feedback means for providing a feedback signal of actual hoist motor operation; and wherein said control signal means includes an operational amplifier having one input connected to the photoresistive element of said photocoupling means and a second input connected to the feedback signal of said feedback means to compare the signals from the first and the second input and, thereby, establish the control signal.
 7. A hoist control systEm as set forth in claim 6 wherein said operational amplifier is a difference amplifier for establishing the control signal in proportion to the difference between the feedback signal and the reference signal.
 8. A hoist control system providing a non-linear control signal for controlling a hoist motor in response to a linear reference signal from a pendant control comprising: manual means for establishing a voltage reference signal directly proportional to a manual adjustment of the pendant control; light source means connected to the pendant control to emit a variable intensity light proportional to the reference signal of said manual means; and receiver means logarithmically responsive to the light of said light source means for establishing a control signal in response to the variable intensity light of said light source means, the control signal of said receiver means thereby being established in a non-linear relation to a linear manual adjustment of said manual means to drive said hoist motor at an increased speed in response to an increased voltage reference signal.
 9. A hoist control system as set forth in claim 8 including a potentiometer mounted in the pendant control to provide a variable voltage signal from the pendant control and wherein said manual means includes an adjustment knob mounted to the pendant control to adjust the voltage signal from said potentiometer in a linear relationship to the movement of the knob of said manual means.
 10. A hoist control system as set forth in claim 9 wherein said receiver means includes a variable resistance material whose resistance changes logarithmically in response to a linear change of the knob of said manual means.
 11. A hoist control system as set forth in claim 10 wherein said light source means includes an incandescent filament lamp which is unresponsive to intermittent voltage changes in said reference signal induced by noise and interference signals being superimposed on said reference signal.
 12. A hoist control system as set forth in claim 8 including: feedback means for providing a signal indicative of actual hoist motor operation; and comparing means for comparing the signal from said feedback means with the control signal from said receiver means to effect hoist operation whenever a difference between the compared signals is detected.
 13. A hoist control system as set forth in claim 12 wherein said feedback means includes a tachometer generator connected to the hoist motor to detect the speed of the motor and the control signal from said receiver means is scaled to indicate desired hoist motor speed. 